Partial Turgor Pressure Regulation in Chara canescens and its Implications for a Generalized Hypothesis of Salinity Response in Charophytes

Concentrations of ions and sucrose in the vacuolar sap of Chara canescens growing in an oligohaline lake (1.5 ‰) were estimated over the main growth period of the plants. During fructification vacuolar sap contained a mean of 41 mol m^?3 (range 10.2–61.8) sucrose. The mean turgor pressure was 239 mosmol kg^?1 (range 219–264). In long- and short-term experiments these plants were subjected to increasing salinities up to 22 ‰. When salinity was increased from 1.5 to 4.4 ‰ turgor pressure was restored to only 80 % of the initial value. This reduced level of turgor pressure was maintained up to a salinity of 22 ‰. The increase in vacuolar osmotic potential was due to the monovalent ions Na⁺, K⁺ and Cl^?. The relative amounts of Na⁺ and K⁺ participating in the regulation process were dependent on external salinity. The regulatory mechanisms observed in the brackish water species Ch. canescens are compared with those reported from freshwater and euryhaline species.     

Seasonal changes of ionic concentrations in the vacuolar sap of Chara vulgaris L. growing in a brackish water lake

Summary The composition of the vacuolar sap of Chara vulgaris growing in a brackish water lake was estimated weekly over 2 years (1984–1985). The ionic concentrations of the main cations Na⁺, K⁺, Ca²⁺, and Mg²⁺ and the anion Cl^- varied depending on cell age, developmental state, and season. The average of all measurements (in mM) was Na⁺: 35, K⁺: 106, Ca²⁺: 7, Mg²⁺: 23, Cl^-: 101, SO _2- ⁴ : 20, and PO _3- ⁴ : 5. At the onset of growth in May/June the ionic content was lower compared to the mean value for the year, steadily increasing until it reached its maximum above the annual mean in winter. During the period of fructification (sexual reproduction: formation of antheridia and oogonia), when up to 100 mM sucrose was accumulated in the vacuolar sap, ionic content was lowest. This resulted in a fairly constant osmotic potential throughout the year. Mg²⁺ and Ca²⁺ concentrations were correlated with the physiological age of the cells.     

Salinity response of a freshwater charophyte, Chara vulgaris

Abstract. Chara vulgaris L. growing in an oligohaline lake was adapted to laboratory conditions and subjected to long-term salinity treatments ranging from 0 to 350 mol m ³ NaCl added to the lake water (40–680 mosmol kg ¹). Osmotic potential and concentration of the main osmotically active solutes (K⁺, Na⁺, Mg²⁺, Cl and sucrose) in the vacuolar sap of the central internodal cells were estimated. C. vulgaris did regulate turgor but incompletely. Turgor decreased from 335 mosmol kg ¹ under control conditions to 52–111 mosmol kg ¹ at 350 mol m ³ NaCl. The enhancement of πⁱ was achieved by increase in both ions and sucrose. Sterile and fertile plants differed in their response to osmotic stress. In sterile plants, the ions accounted for about 87% of the vacuolar osmotic potential. The increase of πⁱ under osmotic stress was exclusively due to an accumulation of Na⁺ and Cl^-. In fertile plants, sucrose accounted for about 35% of πⁱ and ions for about 51% Under osmotic stress, sucrose content increased together with the ionic content of Na⁺ and Cl^-.     

Effects of NaCl on ion relations and carbohydrate status of roots and on osmotic regulation of roots and shoots of Atriplex amnicola

Abstract Atriplex amnicola was grown at 25, 200 or 400 mol m³ NaCl. Root tissues at different stages of development were investigated for concentrations of K⁺, Na⁺ and Mg²⁺, and in some cases for Cl^?. Sugar and starch concentrations were measured for plants grown at 25 or 400 mol m³ NaCl. In the ‘slightly vaeuolated’ root tips, Na⁺ was only 40 mol m^?3 at an external concentration of 400 mol m^?3 NaCl. The concentrations of K⁺ were not affected substantially by external NaCl between 25 mol m^?3 and 400 mol m^?3. The ‘highly vacuolated’ root tissues had substantially higher concentrations of K⁺, Na⁺ and Cl^? in plants grown at 200 and 400 mol m ³ NaCl than in plants grown at 25 mol m^?3 NaCl. Concentrations of Cr and of the sum of the cations in recently expanded tissue were similar to those in the bulk of the roots, consisting mainly of old cells. However, the K⁺: Na⁺ decreased with age; at 400 mol m^?3 external NaCl with a K⁺: Na⁺ of 0.012, the K⁺: Na⁺ in recently expanded 12 mm root tips was as high as 1.6, compared with 0.7 for the bulk of the roots. These ion data were used to estimate cytoplasmic and vacuolar concentrations of K⁺ and Na ⁺. Such calculations indicated that between 25 mol m³ and 400 mol m^?3 external NaCl the concentration of the sum of (Na⁺+K⁺) in the cytoplasm was maintained at about 180–200 mol m^?3 (cell water basis). In contrast, the (Na⁺+ K⁺) concentration in the vacuole was 170 mol m^?3 for plants grown at 25 mol m^?3 NaCl and 420 mol 400 mol m^?3 NaCl. The expanding root (issues exhibited greatly decreased soluble sugars and starch between dusk and dawn. Ai both times, sugar and starch concentrations in these tissues were 2.5–4.0 times greater in plants grown at 400 mol m^?3 NaCl compared with plants grown at 25 mol m^?3 NaCl. In contrast, carbohydrate concentrations in expanded root tissues were very similar at 25 and 400 mol m^?3 and showed little diurnal fluctuation. This paper considers the causes for the slower growth of A. amnicola at 400 than at 25 mol m”³ NaCl, using the data for the roots described here, and those for the shoots presented in the preceding paper (Aslam et al., 1986). There is no support for possible adverse effects by high internal ion concentrations. Instead, there may be deficiencies in supply of organic solutes for osmotic regulation; during part of the night a limited supply of such solutes may well restrict the rate of expansion of cells in plants growing at 400 mol m^?3 NaCl. There is insufficient evidence to decide whether this limitation in the expanding tissues is particularly prominent for the roots or for the shoots.     

Changes in growth and water-soluble solute concentrations in Sorghum bicolor stressed with sodium and potassium salts

Sorghum bicolor L. Moench, RS 610, was grown in liquid media salinized with NaCl, KCl, Na₂SO₄, K₂SO₄ or with variable mixtures of either NaCl/KCl or Na₂SO₄/K₂SO₄ at osmotic potentials ranging from 0 to -0.8 MPa. The purpose was to study the effects of different types and degrees of salinity in growth media on growth and solute accumulation. In 14-day-old plants the severity of leaf growth inhibition at any one level of osmotic potential in the medium increased according to the following order: NaCl < Na₂SO₄ < KCl = K₂SO₄. Inhibition of growth by mixtures of Na⁺ and K⁺ salts was the same as by K⁺ salts alone. Roots responded differently. Root growth was not affected by Na⁺ salts in the range of 0 to -0.2 MPa while it was stimulated by K⁺ salts. The major cation of leaves was K⁺ because S. bicolor is a Na⁺-excluder, while Na⁺ was the major cation in roots except at low Na⁺/K⁺ ratios in media. Anions increased in tissues linearly in relation to total monovalent cation, but not with a constant anion/cation ratio. This ratio increased as the cation concentrations in tissues increased. Sucrose in leaf tissue increased 75 fold in Chloride-plants (plants growing in media in which the only anion of the salinizing salts was Cl^?) and 50 fold in Sulphate-plants (the only anion of the salinizing salts was SO₄^2-). Proline increased 60 and 18 fold in Chloride- and Sulphate-plants, respectively, as growth media potentials decreased from 0 to -0.8 MPa. The concentrations of both sucrose and proline were directly proportional to the amount of total monovalent cation in the tissue. Sucrose concentrations began increasing when total monovalent cations exceeded 100 μmol (g fresh weight)^?1 (the monovalent cation level in non-stressed plants), but proline did not start accumulating until monovalent cation concentrations exceeded 200 μmol (g fresh weight)^?1. Therefore, sucrose seemed to be the solute used for osmotic adjustment under mild conditions of saline stress while proline was involved in osmotic adjustment under more severe conditions of stress. Concentrations of inorganic phosphate, glucose, fructose, total amino acids and malic acid fluctuated in both roots and leaves in patterns that could be somewhat correlated with saline stress and, sometimes, with particular salts in growth media. However, the changes measured were too small (at most a 2–3 fold increase) to be of importance in osmotic adjustment.     

Solute adjustments in leaves of two species of wheat at two different stages of growth in response to salinity

Changes in leaf solute concentrations in response to salinity were measured at two growth stages in two species of wheat, Triticum turgidum L. cv. Aldura (Durum group) and Triticum aestivum L., cv. Probred that differed in their salt tolerances. Both species at 55 days of age were Na⁺-excluders, but the concentration of Na⁺ was 10 times higher in T. turgidum than T. aestivum at low to moderate levels of stress. The ratio then decreased until it was 2:1 at – 1.2 MPa. In T. turgidum, K⁺ concentrations decreased with increasing Na⁺ concentrations so that the sum of the two cations remained constant at all stress levels, but in T. aestivum K⁺ decreased more rapidly than Na⁺ increased. In both species growing in media at 0 to –0.6 MPa, the amounts of Mg²⁺ and Ca²⁺ in 55-day-old plants that could be extracted with hot water were below 0.1 mmol (g dry weight)^?1. Then, as osmotic potentials of media decreased further, hot water-extractable Ca²⁺ increased greatly until, at – 1.2 MPa, Ca²⁺ concentrations were almost equal to the sum of Na⁺ and K⁺. In the range of 0 to –1.0 MPa, the ratio of Cl^? to total cationic charge remained constant at 1:6 in T. aestivum and 1:2 in T. turgidum. However, at – 1.2 MPa, the ratio in both species had changed to 2:3. Sucrose and betaine concentrations were 4 and 48 μmol (g dry weight)^?1, respectively, in non-stressed plants of both species. At – 1.2 MPa, sucrose had increased 30-fold but betaine had increased only 2.5-fold. Proline increased exponentially relative to foliar Na⁺ in T. turgidum. In T. aestivum only plants grown at –1.2 MPa contained sufficient Na⁺ to stimulate the accumulation of proline. Although the quantities of the solutes in leaves of non-stressed 96-day-old plants differed from those in non-stressed younger plants, the patterns of change of organic solutes as the older plants were subjected to increasing saline stresses were the same as in younger plants with the exception of sucrose. Sucrose concentrations were much higher in leaves of non-stressed older plants and this sugar first increased and then decreased with decreasing osmotic potentials of media.     

Relationship between cation accumulation and water content of salt-tolerant grasses and a sedge

Abstract Salt-tolerant grasses and a sedge were grown at three salinities in a controlled-environment greenhouse. They were measured for growth rate, ash content, water content and cations. Fourteen species from the genera Sporobolus, Aeluropus, Leptochloa, Paspalum, Puccinellia, Hordeum, Elymus, Distichlis and Spartina survived up to the highest salt treatment (540 mol m^?3 NaCl). These were designated halophytes. Eleven species from the genera Triticum, Phragmites, Dactylotenium, Cynodon, Polypogon, Panicum, Jovea and Heleocharis only survived up to 180 mol m^?3 NaCl and were designated salt-tolerant glycophytes. All species except Distichlis palmeri grew fastest on the non-saline control treatment. All species tended to have higher Na⁺ contents and lower K⁺ and water contents on saline treatments compared to control plants. Halophytes differed from glycophytes in having statistically significant lower water contents on the non-saline treatment, and lower ash contents and Na:K ratios on 180 mol m^?3. However, the range of values among species was greater than the differences between halophytes and glycophytes. All species appeared to use Na⁺ accumulation and loss of water as the main means of osmotic adjustment. Three halophytic species were grown for a longer period of time to check the above results. The osmolality of the cell sap was measured directly by the vapour pressure method and compared to calculated values based on Na⁺, K⁺ and water contents (and assuming a balancing anion such as Cl^?). Na⁺ and K⁺ alone could account for greater than 75% of the osmotic potential at all salinities. Hence, the accumulation of organic solutes did not appear to be an important factor in the osmotic adjustment of these species. The results support the conclusion that grasses coordinate Na⁺ uptake and water loss to maintain a constant osmotic potential gradient between the shoot tissues and the external solution. The results were compared to a previous study with dicotyledonous halophytes at the same location.     

Effects of external NaCl on the growth of Atriplex amnicola and the ion relations and carbohydrate status of the leaves

Abstract Atriplex amnicola, was grown in nutrient solution cultures with concentrations of NaCl up to 750 mol m^?3. The growth optimum was at 25–50 mol m^?3 NaCl and growth was 10–15% of that value at 750 mol m^?3 NaCl. Sodium chloride at 200 mol m^?3 and higher reduced the rate of leaf extension and increased the time taken for a leaf to reach its maximal length. Concentrations of Na⁺, K⁺ and Mg²⁺ in leaves of different ages were investigated for plants grown at 25, 200 and 400 mol m^?3 NaCl. Although leaves of plants grown at 200 and 400 mol m^?3 NaCl had high Na⁺ concentrations at young developmental stages, much of this Na⁺ was located in the salt bladders. Leaves excluding bladders had low Na⁺ concentrations when young, but very high in Na⁺ when old. In contrast to Na⁺, K⁺ concentrations were similar in bladders and leaves excluding bladders. Concentrations of K⁺ were higher in the rapidly expanding than in the old leaves. At 400 mol m^?3 NaCl, the K⁺:Na⁺ ratios of the leaves excluding bladders were 0.4–0.6 and 0.1 for rapidly expanding and oldest leaves, respectively. The Na⁺ content in moles per leaf, excluding bladders, increased linearly with the age of the leaves; concurrent increases in succulence were closely correlated with the Na ⁺ concentration in the leaves excluding the bladders. Soluble sugars and starch in leaves, stems and buds were determined at dusk and dawn. There was a pronounced diurnal fluctation in concentrations of carbohydrates. During the night, most plant parts showed large decreases in starch and sugar. Concentrations of carbohydrates in most plant organs were similar for plants grown at 25 and 400 mol m^?3 NaCl. One notable exception was buds at dusk, where sugar and starch concentrations were 30–35% less in plants grown at 400 mol m^?3 NaCl than in plants grown at 25 mol m^?3 NaCl. The data indicate that the growth of A. amnicola at 400 mol m^?3 NaCl is not limited by the availability of photosynthate in the plant as a whole. However, there could have been a growth limitation due to inadequate organic solutes for osmotic regulation.     

Effect of fusicoccin on proton co-transport of sugars in the phloem loading of Ricinus communis L.

The loading of [¹⁴C] sucrose into the phloem from the apoplast of hollow Ricinus petioles was stimulated by fusicoccin (FC, 10 mg l⁻¹), by indole-3-acetic-acid (IAA; 10⁻² mol m⁻³) and inhibited by abscisic acid (ABA 10⁻² mol m⁻³) when added to a buffered perfusing solution of 2% sucrose and 30 mol m⁻³ KCl. A proton efflux was detected in the hollow petiole which was stimulated by FC in the presence of K⁺, insensitive to IAA, and inhibited by ABA, when present in the perfusing solution.The observed results are consistent with an H⁺/K⁺ exchange between the phloem sap and the apoplast which is responsible for the high pH and high [K⁺ of phloem saps. The resultant pH gradient between the phloem sap and the apoplast provides the energy for the proton co-transport of sucrose in phloem loading.     

Expression analysis of LeNHX1 gene in mycorrhizal tomato under salt stress

The plant growth, stem sap flow, Na⁺ and Cl^? content, and the expression of vacuolar Na⁺/H⁺ antiporter gene (LeNHX1) in the leaves and roots of tomato under different NaCl stresses (0.5% and 1%) were studied to analyze the effect of arbuscular mycorrhizal fungi (AMF) on Na⁺ and Cl^? accumulation and ion exchange. The results showed that arbuscular mycorrhizal (AM) plant growth and stem sap flow increased and salt tolerance improved, whereas Na⁺ and Cl^? accumulated. Na⁺ significantly decreased, and no significant decline was detected in Cl^? content after AMF inoculation compared with the non-AM plants. The LeNHX1 gene expression was induced in the AM and non-AM plants by NaCl stress. However, AMF did not improve the LeNHX1 level, and low expression was observed in the AM tomato. Hence, the mechanism that reduced the Na⁺ damage to tomato induced by AMF has little relation to LeNHX1, which can export Na⁺ from the cytosol to the vacuole across the tonoplast.     

Photosynthesis, leaf conductance and water relations of in vitro cultured grapevine rootstock in relation to acclimatisation

Leaf net CO₂ uptake and leaf photosynthetic capacity were investigated in micropropagated 41B grapevine rootstock (Vitis vinifera‘Chasselas’×Vitis berlandieri, Mill. De Gr.) plants grown in the presence of four sucrose concentrations (6.25, 12.5, 25.0 or 37.5 g l^?1). Sucrose concentration in the medium during growth in vitro did not affect the leaf photosynthetic performance of plants neither before nor after transplantation. The maximum photosynthetic rate, measured as CO₂-dependent O₂ evolution, was 7.3 µmol m^?2 s^?1 before transplanting and 15.4 µmol m^?2 s^?1 one month after transplantation. The maximum quantum yield of O₂ evolution (on the basis of incident light) was about 0.07 for all sucrose treatments both before and after transplantation. Dry biomass before transplanting was highest in plants grown with 25.0 or 37.5 g l^?1 sucrose in the medium. One month after transplantation the highest dry biomass was also observed for the same treatments. Survival of plants was 100% for all treatments. Leaf conductance to water vapour was always higher in plants before than after transplantation. Both before and after transplanting it increased with increasing light intensity and decreased slightly with increasing CO₂ molar ratio in in vitro plants. Stomata of plants before transplantation were unresponsive to vapour pressure deficit. In vitro plants experience an acute water stress when they are maintained with the whole root system in water and exposed to ambient controlled conditions in a growth chamber. However, there was no wilting of the leaves when similar plants with roots cut off were left in the same conditions. Hydraulic conductivity was low at both root and shoot-root connection levels. It is likely that water supply could be limiting during transplantation because of the low root and root-stem connection conductivity. Water uptake by roots rather than water loss from the shoots would be of primary importance for the maintenance of water balance during acclimatisation.     

Vigor and salt tolerance in 3 lines of tall wheatgrass

The F₁ progeny of the cross of two salt-tolerant lines of Thinopyrum elongatum [Host] D. R. Dewey grew better than either parent under non-saline and saline growth conditions. Under non-saline conditions, the hybrid produced 1.8 times as much vegetative tissue as one parent and 3.2 times more than the other parent in the same length of time. The relative growth rates of the 2 parental lines decreased equally as media osmotic potentials decreased. The relative growth rate of the hybrid did not decrease as rapidly as that of the parents; therefore, it was concluded that the greater growth of the hybrid was due to increased salt tolerance. Carbohydrate reserves and water-soluble solutes believed to be involved in osmotic adjustment were assayed to determine if there were any differences between the hybrid and its parents in their abilities to accumulate these compounds. The concentrations of these constituents were measured at dawn and at dusk of the same day in plants grown in media at osmotic potentials ranging from –0.1 to –1.2 MPa. There were no differences in pool sizes of the organic compounds in the 3 lines. Starch increased 10–40 fold in leaves from dawn to dusk and sucrose increased 100-fold. However, this pattern was unaffected by salinity. Conversely, betaine concentrations increased with increasing salinity but were the same at dawn and dusk. Na⁺ and K⁺ were affected by both light and salinity. Cl was one-half (Na⁺+ K⁺) on a molar basis under all conditions. Proline accumulated when (Na⁺+ K⁺) exceeded 200 μmol (g fresh weight)^?1. Since this amount of (Na⁺+ K⁺) existed only in tissues harvested at dusk from severely saline-stressed plants, only leaves from such plants harvested at dusk contained proline.     

Salt tolerance in Aster tripolium L. III. Na and K fluxes in intact seedlings

Abstract Uptake and transport of Na and K was studied using the radioactive tracers ²²Na and ⁴²K in intact Aster tripolium L. seedlings grown at two salinities CS 10 and CS 100, (containing 10mol m^?1 and 100 mol m^?3 Na, respectively, together with other major ions in the proportions found in sea water). At both salinities a much greater proportion of the Na than K taken up by the plant was subsequently transported to the shoot. Most ⁴²K fluxes were reduced by about 40% in CS 100 plants relative to CS 10 except root accumulation which increased. Experiments involving changing the salinity from CS 10 to CS 100 showed that ⁴²K fluxes remained constant for at least 40 h, indicating that competition with Na for uptake sites was not the cause of the reduced flux in CS 100 plants. ²²Na fluxes responded immediately to a change in salinity with all fluxes increasing six-fold when the salinity was raised. When the salinity was lowered, however, root accumulation returned to the level in CS 10 control plants whereas transport to the shoot was inhibited by the previous high salinity treatment, being reduced to only 35% of the rate in CS 10 plants. The time courses of osmotic adjustment and Na accumulation following an increase in salinity were found to be very similar, with sufficient Na being accumulated to account for the observed increase in sap osmotic pressure.     

Soybean [Glycine max (L.) merrill] embryogenic cultures: The role of sucrose and total nitrogen content on proliferation

Summary To improve proliferation of soybean cultures in liquid medium, the effects of sucrose; total inorganic nitrogen; content of No₃ ⁻, NH₄ ⁺, Ca²⁺, PO₄ ³⁻, K⁺; NH₄ ⁺/NO₃ ⁻ ratio; and medium osmotic pressure were studied using cv. Jack. Sucrose concentration, osmotic pressure, total nitrogen content, and ammonium to nitrate ratio were found to be the major factors controlling proliferation of soybean embryogenic cultures. Growth decreased linearly as sucrose concentration increased from 29.7 mM to 175.3 mM. A sucrose concentration of 29.2 mM, a nitrogen content of 34.9 mM, at 1 to 4 ammonium to nitrate ratio were found to be optimal for the fastest proliferation of soybean embryogenic cultures. There was no significant effect on proliferation of cultures when concentrations of NH₄ ⁺, Ca²⁺, PO₄ ³⁻, and K⁺ were tested in the range of 3.50 to 10.50, 1.02 to 3.06, 0.68 to 2.04, and 22.30 to 36.70 mM, respectively. The relative proliferation of embryogenic cultures of four soybean genotypes was evaluated in Finer and Nagasawa medium and in the new medium formulation. Despite genotype-specific differences in growth, the genotypes tested showed a biomass increase in the new formulation equal to 278, 269, 170, and 251% for Chapman, F138, Jack, and Williams 82, respectively, relative to their growth on standard FN medium. Due to its lowered sucrose and nitrogen content, we are referring to the new medium as FN Lite.     

Nitrogen nutrition and the level of Crassulacean acid metabolism in Kalanchoë lateritia Engl.

Abstract. The influence of different nitrogen levels was studied in the CAM facultative Kalanchoë lateritia by watering some plants with Hoagland's solution (which contains, besides other ions, NO₃^?= 14.47mol m^?3and NH₄⁺= 1.04mol m^?3; N group), and others with the same solution but with combined nitrogen concentration reduced to either one fifth (NO₃^?= 2.894mol m^?3 and NH₄⁺= 0.208mol m^?3; N/5 group) or one tenth (NO₃^?= 1.447mol m^?3and NH₄⁺= 0.104mol m-³;N/10 group). The influence of the three nitrogen levels on CAM expression was assessed through activities of PEP-Case, PPD and RuBisCo, diurnal fluctuation of titratable acidity, mesophyll succulence, soluble protein, chlorophyll, nitrate, starch contents, pattern of nocturnal CO₂ exchange and electron microscopy. CAM photosynthesis was more intense in N/5 plants which also had the highest Sm value. The activity of RuBisCo showed no significant differences in the three situations (expressed on chlorophyll basis) whereas both PEP-Case and PPD had higher values in N/5” plants. Chlorophyll and soluble protein were more abundant in the N plants followed by N/5 and N/10 plants. Nitrate was higher in N plants and starch content in N/5 plants. IRGA determination of CO₂ nocturnal uptake showed that N/5 plants began CO₂ capture earlier and at a more intense rate and for a longer period than plants from other groups also having a daily variation of titratable acidity (97.71 ± 10.8 μeq. G^?1 f.w.) indicative of performing strong CAM. Electron microscope morphometric analysis revealed larger chloroplasts in N plants and smaller in N/10 plants, with starch fractional volume higher in N/5 plants, correlating with more intense CAM activity of these plants.     

Influence of Cotyledon Excision and Sucrose on Root Formation in Pea Cuttings

Sucrose was supplied to stock plants of Pisum sativum L. cv. Alaska grown at different levels of irradiance. There was no significant effect on the rooting of the cuttings by sucrose supply to intact plants regardless of the irradiance. However, an increase in the number of roots per cutting was obtained at increasing concentrations of sucrose when the stock plants had been grown at 4 W m^?2 and their cotyledons had been removed two days before the cuttings were excised. Cotyledons were removed from stock plants at different times before the excision of cuttings with the intent to regulate the endogenous supply of carbohydrate. The number of roots per cutting was reduced by removal of the cotyledons and this reduction was correlated to the number of days the stock plants had grown without cotyledons as well as to the irradiance pre-treatment. A greater reduction occurred in cuttings from plants grown under 4 W m^?2 than from those grown under 38 W m^?2. The growth of the stock plants and the subsequent stem growth of the cuttings was determined by the irradiance to the stock plants and by the time of removal of the cotyledons. Exogenous supply of sucrose had no effect on the stem growth of the cuttings.     

Salt tolerance of prickly pear cactus (Opuntia ficus-indica)

In view of the need to exploit saline water resources in agriculture in arid zones, we investigated the salt tolerance of Opuntia ficus-indica in plants growing in solution culture. Salt (NaCl) was added in concentrations ranging from 5 (control) to 200 mol m^-3. Cladode growth was sensitive to salinity, being 60% of the control at 50 mol m^-3 NaCl. The root-to-stem ratio decreased significantly only at 200 mol m^-3. Various other parameters were studied, such as water content, Na, K and Cl content, osmotic pressure, and CO₂ uptake. Of these parameters the decreases in cladode water content and CO₂ uptake were related to the decrease in cladode growth. Raised salinity increased cladode osmotic pressure, which was associated with tissue dehydration. We concluded that osmotic adjustment does not occur in prickly pear under salt stress.     

Increase in cytoplasmic calcium content in internodal cells of Lamprothamnium upon hypotonic treatment

Abstract Internodal cells of Lamprothamnium succinctum, a brackish water Characeae, regulate turgor pressure in response to changes in external osmotic pressure (turgor regulation). When internodal cells were transferred to a hypotonic medium containing 3.9 mol m^?3 Ca²⁺, the cell osmotic pressure decreased and the original turgor pressure was recovered. During turgor regulation Ca content of the cytoplasm increased significantly. Lowering the external Ca²⁺ concentration from 3.9 to 0.01 mol m^?3 inhibited this increase in cytoplasmic calcium content. In a hypotonic medium containing 0.01 mol m^?3 Ca²⁺, turgor regulation was inhibited as previously reported (Okazaki & Tazawa, 1986a). Thus transient increase in cytoplasmic Ca, probably in the ionized form, induced by hypotonic treatment may play an important role in turgor regulation.     

Phosphate cycles in energy crop systems with emphasis on the availability of different phosphate fractions in the soil

The growing cells of hydroponic maize roots expand at constant turgor pressure (0.48 MPa) both when grown in low-(0.5 mol m^-3 CaCl₂) or full-nutrient (Hoagland's) solution and also when seedlings are stressed osmotically (0.96 MPa mannitol). Cell osmotic pressure decreases by 0.1–0.2 MPa during expansion. Despite this, total solute influx largely matches the continuously-varying volume expansion-rate of each cell. K⁺ in the non-osmotically stressed roots is a significant exception-its concentration dropping by 50% regardless of the presence or absence of K⁺ in the nutrient medium. This corresponds to the drop in osmotic pressure. Nitrate appears to replace Cl^- in the Hoagland-grown cells.Analogous insensitivity of solute gradients to external solutes is observed in the radial distribution of water and solutes in the cortex 12 mm from the tip. Uniform turgor and osmotic pressures are accompanied by opposite gradients of K⁺ and Cl^-, outwards, and hexoses and amino acids, inwards, for plants grown in either 0.5 mol m^-3 CaCl₂ or Hoagland's solution (with negligible Cl^-). K⁺ and Cl^- levels within both gradients were slightly higher when the ions were available in the medium. The gradients themselves are independent of the direction of solute supply. In CaCl₂ solution all other nutrients must come from the stele, in Hoagland's solution inorganic solutes are available in the medium.24 h after osmotic stress, turgor pressure is recovered at all points in each gradient by osmotic adjustment using organic solutes. Remarkably, K⁺ and Cl^- levels hardly change, despite their ready availability. Hexoses are responsible for some 50% of the adjustment with mannitol for a further 30%. Some 20% of the final osmotic pressure remains to be accounted for. Proline and sucrose are not significantly involved. Under all conditions a standing water potential step of 0.2 MPa between the rhizodermis and its hydroponic medium was found. We suggest that this is due to solute leakage.Abbreviations EDX energy dispersive X-ray microanalysis - water potential - 11-1 cell osmotic pressure - P turgor pressure     

Enhancement of seed germination in high salinity by engineering mannitol expression in Arabidopsis thaliana

The bacterial gene mtlD, which encodes mannitol 1-phosphate dehydrogenase (E. C. 1. 1. 1. 17), was transformed into Arabidopsis thaliana and expressed under control of the CaMV 35S promoter. MtlD-transformants accumulated mannitol, a sugar alcohol that is not normally found in Arabidopsis. Amounts of soluble carbohydrates, sucrose, glucose, fructose, myo-inositol and mannitol were determined in different tissues of wild-type and transgenic plants. We estimated that less than 1& of the carbon assimilated was converted into mannitol by the transgenic plants. The establishment of individual transformed lines (after self-crossing three times) resulted in high and low mannitol-producing lines which were stably maintained. The presence of mannitol did not alter plant appearance or growth habit. When MtlD-expressing seeds and control seeds (T3 generation) were imbibed with solutions containing NaCl (range 0 to 400 mol m^?3), transgenic seeds containing mannitol germinated in medium supplemented with up to 400 mol m^?3 NaCl, while control seeds ceased germination at 100 mol m^?3 NaCl. It is doubtful whether the ability to germinate in high salt was a result of an osmotic effect exerted by elevated levels of mannitol, considering that mannitol concentrations were in the mol m^?3 range in seeds. A specific effect of polyols, for example on the integrity of subcellular membranes or enzymes, cannot be excluded.